Touch sensor systems, such as touchscreens or touch monitors, can act as input devices for interactive computer systems used for various applications, for example, information kiosks, order entry systems, video displays, etc. Such systems may be integrated into a computing device, thus providing interactive touch capable computing devices, including computers, electronic book readers, mobile communications devices, and other touch sensitive devices including robots.
Generally, touch sensor systems enable the determination of a position on the surface of a substrate via a user's touch of the surface. For some applications such as track pads or touch sensitive robotic shells, the substrate may be made of an opaque material such as a metal. When the touch sensor is a transparent touchscreen, the touch substrate is typically made of some form of glass which overlies a computer or computing device display, like a liquid crystal display (LCD), a plasma display, etc. The touch sensor system is operatively connected to the device display so that it also enables the determination of a position on the device display and, moreover, of the appropriate control action of a user interface shown on the display.
Touch sensor systems may be implemented using different technologies. Acoustic touch sensors, such as ultrasonic touch sensors using surface acoustic waves, are currently one of the major touch sensor technologies and many types of acoustic touch sensors now exist. FIG. 1a shows a front plan view of a substrate 2 of a “non-Adler-type” acoustic touch sensor 1. A perimeter region 3 of the front surface 4 substrate 2 surrounds an interior touch region 5 of the substrate 2. A number of transducers 6a, 6b, 6c, 6d, such as wedge transducers, are bonded to the front surface 4 in the perimeter region 3. The touch sensor 1 uses a plurality of transducers per coordinate axis to spatially spread respective transmitted surface acoustic wave signals (e.g., shown in a solid line arrows 7a, 7b) and determine the touch region 5 coordinates. For example, for the X coordinate axis, X-axis transmitting transducers 6a at a respective perimeter region 3 generates surface acoustic wave pulses that propagate in the Y direction across the substrate 2 (across the touch region 5) along plural parallel paths to X-axis receiving transducers 6b disposed on the opposite perimeter region 3 where the waves are received for processing. The X coordinate of a touch in touch region 5 is determined by which of the transmit/receive transducer pairs corresponds to surface acoustic wave intercepted by the touch. Similarly, for the Y coordinate axis, Y-axis transmitting transducers 6c at a respective perimeter region 3 generates surface acoustic wave pulses that propagate in the X direction across the substrate 2 (across the touch region 5) along plural parallel paths to Y-axis receiving transducers 6d disposed on the opposite perimeter region 3 where the waves are received for processing. The Y coordinate of a touch in touch region 5 is determined by which of the transmit/receive transducer pairs corresponds to surface acoustic wave intercepted by the touch. The transducer arrangement provides a grid pattern to enable two-dimensional coordinates of a touch on the touch region 5 to be determined. Touching the touch region 5 at a point causes a loss of energy by the surface acoustic waves passing through the point of touch. This is manifested as an attenuation of the surface acoustic waves. Detection circuitry associated with each receiving transducer 6b, 6d detects the amplitudes of the surface acoustic wave signals and observes which transmit/receive transducer pairs have perturbed or attenuated signals as a means to determine the surface coordinates on the touch region 5. A controller (not shown) drives the operation of the transducers 6 and provides the touch coordinates to an operating system and software applications to provide the required user interface with a display operably connected to the transducers 6. Note that the touch sensor 1 is illustrated as flat and rectangular, but may take on different shapes and configurations depending upon the application.
An “Adler-type” acoustic touch sensor uses only two transducers per coordinate axis to spatially spread a transmitted surface acoustic wave signal and determines the touch surface coordinates by analyzing temporal aspects of a wave perturbation from a touch. For each axis, one transducer at a respective peripheral surface generates surface acoustic wave pulses that propagate through the substrate across a perpendicular peripheral surface along which a first reflective grating or array is disposed. The first reflective array is adapted to reflect portions of a surface acoustic wave perpendicularly across the substrate along plural parallel paths to a second reflective array disposed on the opposite peripheral surface. The second reflective array is adapted to reflect the surface acoustic wave along the peripheral surface to a second transducer at a respective perpendicular peripheral surface where the wave is received for processing. The reflective arrays associated with the X axis are perpendicular to the reflective arrays associated with the Y axis so as to provide a grid pattern to enable two-dimensional coordinates of a touch on the substrate to be determined. Touching the substrate surface at a point causes a loss of energy by the surface acoustic waves passing through the point of touch. This is manifested as an attenuation of the surface acoustic waves. Detection circuitry associated with each receiving transducer detects the attenuation as a perturbation in the surface acoustic wave signal and performs a time delay analysis of the data to determine the surface coordinates of a touch on the substrate.
Historically, devices utilizing an acoustic touch sensor, like a touchscreen and touch pad products, were associated with a protective bezel. An acoustic touch sensor may have a large number of operative elements (either multiple transducers, or transducer and reflective array combinations) disposed on, and along, the front peripheral surfaces of the substrate. In order to prevent damage due to exposure from the environment or external objects, the housing for these sensors or for the devices integrating a sensor may include a bezel that hides and protects these peripheral operative elements, so that only an active touch region on the front surface of the substrate is exposed for possible touch input.
Current trends eliminate the bezel in favor of flush surroundings of touch area. This market trend is also affecting touch input devices of larger desktop sizes as indicated by the market interest for zero-bezel SAW touchscreens in the 20-inch and larger size range. Looking further into the future, as imagined by some visionaries of “ubiquitous computing”, currently passive objects like glass table tops could become touch input devices. Furthermore, even now there are hints of cross-fertilization between touch technology and robotics and perhaps future SAW touch technology may find a use endowing robots with a sense of touch in their exterior shells. All these trends and possible extrapolations of touch technology into the future motivate moving transducers and arrays of SAW touch sensors from the exterior touch sensing surface of the substrate to the protected and hidden interior surfaces of the touch substrate.
Acoustic touch sensors may utilize a rounded-substrate-edge approach to obtain such a zero-bezel or bezel-less design. Such sensors operate by using transmitting elements on the back surface that propagate surface acoustic waves around respective curved substrate edges, across the front surface, and around opposite curved substrate edges to reach the receiving elements on the back surface. Bezel-less acoustic touch sensors may enlarge the active touch region to essentially the whole front surface of the substrate, which may be beneficial for a variety of touch input applications from small-sized integrated devices like a smartphone or a tablet computer to a desktop computer and larger touch applications. Further, the combination of protected internal transducers and arrays plus sensitivity for essentially the whole exposed surface is of interest for touch sensitive robotic shells.
FIG. 1b shows a simplified cross-sectional view of an acoustic touch sensor 10 having curved substrate edges. The touch sensor 10 comprises a substrate 11 with a front surface 12, a back surface 15, and connecting end surfaces 20 joining the peripheral regions 14 of the front surface 12 and of the back surface 15. A connecting end surface 20 need not be curved as shown but generally can have any shape that supports transfer of surface acoustic waves between the front and back surfaces 12, 15. The substrate 11 is typically made of some form of glass which overlies a computer display or computing device display 25, like a liquid crystal display (LCD), a cathode ray tube (CRT), a plasma display, etc. In a bezeled surface acoustic wave touch sensor, the peripheral region 14 of the front surface 12 is covered by a bezel provided by the housing of the touch sensor 10 or the device integrating the sensor 10, since the transducers and reflective arrays are on the front surface 12 of the substrate 11. In a bezel-less surface acoustic wave touch sensor, which is shown in the figure, the peripheral region 14 of the front surface 12 is merely the outer/peripheral portion of the front surface 12 and no bezel is required of the associated housing as there are no exposed transducers and reflective arrays. Note that the terms “bezeled” and “bezel-less” are used to connote touch sensors that when installed respectively either require, or do not require, a bezel covering the perimeter of the substrate in order to protect arrays and transducers. Bezel-less surface acoustic wave touch sensors are described in more detail in commonly-owned U.S. Published Application 2011/0234545, entitled “Bezel-less Acoustic Touch Apparatus”, which is herein incorporated by reference. Object 30 is seen in FIG. 1b as a finger, but it is recognized that touches sensed by the surface acoustic waves may include a stylus pressing against the front surface 12 directly or indirectly, through a cover sheet or like element, depending upon the application of the touch sensor 10. Acoustic transducers 35 and reflective element arrays 40 are provided on, and hidden by, a border layer 27 of opaque paint or ink in the peripheral region 14 of the back surface 15. The transducers 35 are operably coupled to a controller or control system 29 (which may be part of a system processor in some embodiments) that is also operably coupled to the display 25. The controller or control system 29 drives the operation of the transducers 35 and measures the signals from such transducers to determine the touch coordinates, which are then provided to an operating system and software applications to provide the required user interface with the display 25.
The curved substrate edges however require particular precision to manufacture. Parasitic signals may otherwise form if the edges are not machined with perfect radii. This, in turn, makes the manufacture of the substrate more costly than conventional, straight-edged substrates. Also, as described in FIG. 1b, in many bezel-less sensors that have certain aesthetic considerations, the periphery of the back surface of the substrate may have an opaque ink or paint applied thereon with the peripheral operative elements being printed on top of the “border ink” in order to hide the elements from view through the typically transparent substrate. For these sensors, the curved edges of the substrate do not allow for the border ink to be applied entirely to the ends of the back surface, which then have to be made opaque in some other manner. For small-sized integrated devices (i.e., mobile or handheld SAW products), the substrate would not have its edging exposed and instead would typically be mounted flush with the device's protective cover on the outside edge. However, this mounting would be easier and, likely, more effective if the sensor has non-curved substrate edges. Acoustically active rounded outside edges may also be problematic in other SAW touch sensor applications, for example, a touch sensitive robot shell made of a tiling of metal SAW touch sensors where a water tight seal is desired where outside edges of component sensors meet.